Synthetic construction matting

ABSTRACT

A method of producing extruded synthetic lumber for use in construction matting comprising the steps of first, providing a blend of ground synthetic particles, the blend selected from the group comprising primarily ground high density polyethylene particles and ground polyethylene terephthalate particles in an amount not more than 99.0 percent by weight and a composition of ground styrene-butadiene rubber comprised primarily of tire buffings in an amount from 1.0 percent to about 3.5 percent by weight. The blend is mixed, heated and extruded into dimensional lumber and then cooled. The resulting lumber has a low retained memory and reduced electrosstatic potential.

[0001] This is a continuation of U.S. patent application Ser. No.09/628,909 filed Jul. 31, 2000.

FIELD OF INVENTION:

[0002] The present invention relates to materials used in fabricatingtemporary access mats and matting systems and, more particularly,presents a unique formulation of synethetic materials for use in mattingfor temporary roads and work surface areas.

BACKGROUND OF THE INVENTION

[0003] Wooden mats have traditionally been utilized in the oil and gasand construction industries to form temporary roads and access areas atdrill site locations and other construction sites. Such wooden matsprovide a temporary foundation for construction vehicles and forconstruction equipment such as cranes and draglines. The temporary roadsand access areas are formed by laying individual wooden mats in adesired pattern. This pattern of individual mats provides access overand around work areas with poor soil conditions that would otherwise beinaccessible to heavy trucks and construction equipment. When thedrilling or construction is completed these mats can be removed forutilization elsewhere.

[0004] Wooden mats are also used in many marine applications. Suchapplications, include the use of wooden mats or matting to cover thedecks of ships, barges and other marine vessels. Wooden matting is alsoused in the construction of docks, harbors and walkways around suchmarine structures.

[0005] The use of wooden mats present certain disadvantages. The matsare typically made of layers of wood timbers spiked or bolted together.The timbers forming the mats are subject of splitting, warping, breakageand disposal in compliance with state and federal regulations. Matshaving split, broken or warped surfaces can produce imperfections in thematted surfaces that impede the access of the heavy equipment or causedamage to the equipment. The wooden mats used to form the mattedsurfaces are also expensive, require substantial maintenance, andincrease the demand on forests that produce timber and timber products.Wooden mats are also heavy and can be difficult to move, place andstore.

[0006] Applicants' herein propose formulas for blending a combination ofsynthetic structural materials to produce structural members for use inthe construction of mats and matting systems. U.S. Pat. No. 5,653,551 toSeaux suggests a mat system having individual mats comprised ofcomposite materials. Seaux proposes a combination of virgin resins,plastics, re-claimed polyolefins and vulcanized rubber in furthercombination with strengthening agents such as fiberglass, steel,graphite, nylon or combinations of the materials. However, the Seauxpatent makes no suggestion as to a preferred proportion or combinationof such composite materials to be used in forming the mat.

[0007] There are many problems associated with the use of structualmembers comprising synthetic materials in the formation of constructionmatting. Construction matting is subjected to heavy vehicle loads and,more often than not, is used in areas where poor soil conditions areprevelent. Such mats must be sufficiently rigid to distribute thevehicle loading over the matted area and yet be elastic enough to retainthe shape of the matting.

[0008] The loads encountered at a typical construction site oftenproduce pronounced deflections in mats constructed of structural memberscomposed of synthetic materials. Such mats, as a product of such loadsand deflection, often retain too much “memory” which results in thecreation of a permanent deformation in the matting. This retained memoryor deformation reduces the mats ability to distribute the traffic loadsto the soil surface and such retained deformation may require frequentreplacement of the mats.

[0009] The use of synthetic materials in structural materials formatting may also enhance the electrostatic properties of the matting andthus increase the incidence of sparking with a resulting increased riskof explosion. Mats constructed from structural members made with certainsynthetic materials may also present problems due to separation ofcomponent parts of the mat when conventional fasteners such as screws,spikes or bolts are used to secure the mat components together. TheSeaux patent does not present a formulation of synthetic materials toaddress these problems.

[0010] Others have suggested the use of synthentic materials,particularly waste plastics and elastomers, for making constructionmaterials. Examples of such are described in U.S. Pat. No. 5,030,662 toBanerjie and U.S. Pat. No. 5,759,680 to Brooks. Both the Banerjie andBrooks patents primarily feature the use of various polyethylenes as thebulk of the matrix forming structural member. The Banerjie patentteaches the use of polyolefins in conjunction with compatibilizers,impact modifiers and reinforcing agents in the matrix forming thestructural member. The Brooks patent teaches the use of polyolefins inconjunction with cellulosic fibers in the matrix of the structuralmember. Neither patent presents a formulation of synthetic materials toaddress the aforementioned problems presented when such syntheticmaterials are used to produce structural members for use in constructionmatting.

[0011] Scrap rubber has also been suggested for use as a component inthe formulation of synthetic building materials. In U.S. Pat. No.5,439,735 to Jamison rubber is suggested as a component material forparticle board products, because of its resistance to decay, water, rot,insects, and its thermal and acoustic properties.

[0012] In U.S. Pat. No. 4,244,841 to Frankland a method of usinggrindings of scrap tire rubber is proposed for producing structures suchas paving stones, floor coverings, resilient bumpers for highwayguardrails, and railroad tie pads. In U.S. Pat. No. 4,851,500 to Lalwaniteaches a process for blending scrap as a component of the material usedin making roofing, walkway pads, and tiles. U.S. Pat. No. 5,886,078 toSullivan et al. discloses the use of polymeric composites comprisingthermoplastic polyolefins, a rubbery polymeric component such asstyrene-butadine rubber in amounts greater than 4.0 percent by weightand reinforcing filler as a replacement for wood for use as railroadties.

[0013] None of the aforementioned disclose the unique combination ofrubber and synthetic components having the structural and physicalproperties of flexibility, the resiliencey and reduced retained loadmemory and the low electrostatic characteristics that were found byapplicants to be suitable for temporary matting to be used in the oiland gas and in the construction industries.

SUMMARY OF INVENTION

[0014] The present invention presents a unique formulation for syntheticstructural material blended and extruded primarily from high densitypolyethylene (HDPE), polyethylene terephthalate (PET), andstyrene˜butadiene rubber (SBR). The unique formulations presentedherein, when appropriately specified and blended, offer structurebuilding materials that are long lived, flexible, without retaining load“memory” and that are resistant to ultraviolet light, ozone, weather,insect and microbial degradation and electrostatic buildup. A furtherdesired characteristic of the structural materials blended and extrudedas described and claimed herein is that such materials have a lowelectrostatic potential. This reduces the incidence of sparks associatedwith electrostatic potential and as a result reduces the chance ofassociated explosion and fire.

[0015] The formulations described and claimed herein also impartqualities to the structural members so produced that facilitate theiruse as construction material as they accommodate the use of traditionaltools and traditional fasteners such as spikes, nails, screws and bolts.In addition, the formulations described and claimed result in producingstructural materials having excellent compressive, shear and tensilestrength, and high moduli of elasticity and rupture as determined byASTM standard test methods.

[0016] While the precise amounts of each of the components above mayvary according to the desired properties of the ultimate matrix, andwhile particle sizes and particle preparation may affect thecharacteristics of the final product material, it is thought that theformulations instructed herein, within the general range, andpercentages of materials described, will achieve the specific listed anddesired material characteristics for use as construction matting.

[0017] The primary components of Applicants' formulations, high densitypolyethylene (HDPE), polyethylene terephthalate (PET), andstyrene˜butadiene rubber (SBR), can be obtained from virgin materialsmanufacturers and/or distributors. In addition to component availabilitythrough new material suppliers, these components are widely availablethrough recovered materials markets. The reutilization of these polymersis widely recognized to be of paramount importance to conserve energy,landfill space, and other resources given that such materials representa considerable percentage of the overall waste stream and volumes aregenerally increasing every year. Although many modern compositematerials that specify SBR prefer to utilize “devulcanized” feed stocksowing to their much improved cross-linking/bonding abilities, for mostof the applications addressed herein, simple, physical preparations anddetail to particle size results in products achieving the desiredcharacteristics.

[0018] Ground or granulated rubber from vehicle tires known as “tirebuffings” and particulary tire buffings made from truck tire treadsprovide an adequate and desirable source of SBR for use in Applicants'formulations. In addition to SBR, tire buffings may include naturalrubber, cis-polybutadiene rubber and cis-polyisoprene rubbers. Tirebuffings also typically include accelerators such as zinc oxide, leadmonoxide, magnesium oxide, stearic acid, oleic acid and pine tar;antioxidants including paraminophenol, phenyl-alphanaphthylamine,phenylbetanaphthylamine; carbon disulfide as an anti-ozone additive;sulfur as a vulcanization agent for the natural rubber components; andcarbon black as a reinforing material that imparts high tensile strengthto the rubber combination to increase its resistance to abrasion andcutting and reduce electrostatic potential. When tire buffings are usedas source of the SBR composition set forth in Applicants' formulations,the tire buffings serve to impede the build up of static electricity instructural members produced with the formulations and the incidence ofsparks associated with the structural members so produced.

DESCRIPTION OF PREFERRED EMBODIMENTS FORMULA I

[0019] It is thought that structural members extruded to a desired sizefrom the formulations consisting primarily of the following componentmaterials, in the following proportions, ground to a desired particlesize and blended together by weight in the absence of water (i.e., <0.5%by weight) would be suitable for use in construction matting and wouldhave the desired characteristics of reduced electrostatic potential andreduced load memory: COMPONENT RANGE OF PREFERRED PERCENTAGE FORMULA IHDPE At least 90.0 percent by weight An SBR composition In the range of1.0-3.5 percent by weight comprised primarily of tire buffings FORMULAII PET At least 90.0 percent by weight An SBR composition In the rangeof 1.0-3.5 percent by weight comprised primarily of tire buffings

[0020] PET and HDPE may be used as a filler in Formula I or Formula II,respectively. The components in Formula I and Formula II should be mixedin the specified range of percentages, then heated and extruded intodimensional lumber and then cooled in a water bath. While a precisegrinding or gradation of component particles comprising the blend ofFormula I and Formula II is not thought to be required, the particlesize so blended would be thought to pass a 2.5 cm sieve.

[0021] It is thought that the materials as listed and described inFormula I and Formula II when blended as described would produced asynthetic lumber building material with the structural characteristicsshown in Table I when tested as indicated: TABLE I PROPERTY TEST METHODRANGE OF VALUES Modulus of Elasticity ASTM D790 140,000 psi-183,000 psiTensile Strength ASTM D198  1,453 psi-1,587 psi

FORMULA III

[0022] As an alternative embodiment, it is thought that structuralmembers extruded to a desired size from a formulation consistingprimarily of the following component materials, in the followingproportions, ground to a desired particle size and blended together byweight in the absence of water (i.e., <0.5% by weight), would besuitable for use in construction matting and have the desiredcharacteristics of reduced electrostatic potential and reduced loadmemory: COMPONENT RANGE OF PREFERRED PERCENTAGE HDPE in an amount notmore than 75.0 percent by weight An SBR in the range of 1.0-3.5 percentby weight composition comprised primarily of tire buffings PET in anamount not more than 40.0 percent by weight

[0023] It is thought that the components in Formula III when mixed andblended in the specified range of percentages and then heated andextruded into dimensional lumber and then cooled in a water bath wouldalso produce a synthetic lumber with a desired electrostatic potentialand with the a desired structural flexibility and load memory.

[0024] One of significant characteristic of the synthetic lumber boardsextruded from the blends in accordance with the above formulas is thatit is thought that the electrostatic potential of the synthetic lumberwill be lowered by increasing the amount of tire buffings. However, thedesire to achieve the characteristic of a lower electrostatic potentialfor the synthetic lumber must be balanced with the resulting increase inflexibility and, consequently, the increase in the retained “memory”from a deflection or deformation of the synthetic lumber under loadingimparted when the amount of tire buffings utilized in the blend isincreased.

[0025] It is thought that synthetic structural members produced from thematerials specified and blended as described herein would produceconstruction matting that, when exposed to the environment, would longout live construction matting produced with popular alternatives such asmatting made from wood or from “single component” recovered plastics. Inaddition, and as a consequence of the lowered electrostatic potential ofthe formulations, matting made from the composite materials outlinedherein could be safely utilized in environments where electrostaticarching must be avoided (i.e., hazardous materials storage areas, oiland gas locations and other potentially explosive/flammable areas).

[0026] It is thought that the formulations for synthetic structuralmaterial and method of the present invention and many of its attendantadvantages will be understood from the foregoing descriptions. It isalso thought that various changes or modifications may be made to themethods and formulations presented without departing from the spirit andscope of the present invention.

1. A method of producing a synthetic structural material for use inconstructing mats for temporary roads and access areas, which comprisesthe step of producing an extruded synthetic structural member comprisingprimarily: (i) synthetic material selected from the group consisting ofhigh density polyethylene and polyethylene terephthalate in an amountnot more than 99.0 percent by weight; and (ii) a composition ofstyrene-butadiene rubber comprised primarily of tire buffings in therange from 1.0 percent to about 3.5 percent by weight.
 2. A method ofproducing a synthetic structural material for use in constructing matsfor temporary roads and access areas as recited in claim 1 wherein, saidhigh density polyethylene, said polyethylene terephthalate and saidcomposition of styrene-butadiene rubber comprised primarily of tirebuffings, when combined, have a water content of less than 0.5 percentby weight.
 3. A method of producing a synthetic structural material foruse in constructing mats for temporary roads and access areas as recitedin claim 2 wherein, said range of said composition of styrene-butadienerubber comprised primarily of tire buffings is from about 2.0 percent toabout 3.5 percent by weight.
 4. A method of producing a syntheticstructural material for use in constructing mats for temporary roads andaccess areas, which comprises the step of producing an extrudedsynthetic structural member comprising: (i) ground high densitypolyethylene in an amount greater than 90.0 percent by weight; and (ii)a composition of ground styrene-butadiene rubber comprised primarily oftire buffings in an amount from about 1.0 percent to about 3.5 percentby weight.
 5. The method of producing a synthetic structural materialfor use in constructing mats for temporary roads and access areas asrecited in claim 4 wherein, said high density polyethylene and saidcomposition of styrene-butadiene rubber comprised primarily of tirebuffings, when combined, have a water content of less than 0.5 percentby weight.
 6. The method of producing a synthetic structural materialfor use in constructing mats for temporary roads and access areas whichcomprises the step of producing an extruded synthetic structural membercomprising: (i) ground high density polyethylene in an amount not morethan 75.0 percent by weight; (ii) a composition of groundstyrene-butadiene rubber comprised primarily of tire buffings in therange from about 2.0 percent to about 3.5 percent by weight; and (iii)ground polyethylene terephthalate in an amount not more than 40.0percent by weight.
 7. A method of producing extruded synthetic lumbercomprising the steps of: (i) first, providing a blend of groundsynthetic particles, said blend comprising primarily ground syntheticparticles selected from the group consisting of ground high densitypolyethylene particles and ground polyethylene terephthalate particlesin an amount not more than 99.0 percent by weight of said blend and acomposition of ground styrene-butadiene rubber comprised primarily oftire buffings in an amount from 1.0 percent to about 3.5 percent byweight of said blend; (ii) next, mixing said blend; (iii) then, heatingsaid blend; and (iv) extruding said blend into dimensional lumber; and(v) then cooling said extruded dimensional lumber.
 8. The method ofproducing extruded synthetic lumber as recited in claim 7 wherein, saidrange of said ground styrene-butadiene rubber comprised primarily oftire buffings is from 2.0 percent to 3.5 percent by weight.
 9. Themethod as recited in claim 8 wherein said particles of said blend ofground synthetic particles are sized to pass a 2.5 cm sieve.
 10. Themethod of producing extruded synthetic lumber as recited in claim 9wherein, said blend of ground synthetic particles has a water content ofless than 0.5 percent by weight.
 11. A method of producing syntheticmats for temporary roads and access areas, which comprises the step ofproducing an extruded synthetic structural member from a blend of groundsynthetic material, said blend of ground synthetic material comprising:(i) a composition consisting primarily of ground high densitypolyethylene in an amount greater than 90.0 percent by weight; (ii) acomposition consisting primarily of ground styrene-butadiene rubbercomprised primarily of tire buffings in an amount from 1.0 percent to3.5 percent by weight; and (iii) a composition consisting primarily ofground polyethylene terephthalate as a filler.
 12. The method as recitedin claim 11 wherein, in said blend of ground synthetic material, saidcomposition of ground high density polyethylene and said composition ofground polyethylene terephthalate, together, is no more than 99.0percent by weight of said blend and said composition consistingprimarily of ground styrene-butadiene rubber comprised primarily of tirebuffings is in the range from about 1.0 percent to about 3.5 percent byweight of said blend.
 13. The method as recited in claim 12 wherein saidstep of producing said extruded synthetic structural member from saidblend of ground synthetic material includes the steps of: (i) mixingsaid blend; (ii) then, heating said blend; (iv) then, extruding saidblend into dimensional lumber; and (v) then cooling said extrudeddimensional lumber.
 14. The method as recited in claim 13 wherein blendof ground synthetic material is sized to pass a 2.5 cm sieve.
 15. Themethod as recited in claim 14 wherein said blend of ground syntheticmaterial has a water content of less than 0.5 percent by weight.